2019-09-05 链接外部样式表base_css

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    <title>Document</title>
    <!-- 链接外部样式表 -->
    <link rel="stylesheet" href="css/style.css">
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    <!-- <h1 id="abc">这是一个标题标签</h1>
    <h1 id="def">这是一个标题标签</h1>
    <h1 class="box1">这是一个标题标签</h1>
    
    <div class="box1">这是一个div</div>
    <div class="box2">这是一个div</div> -->

    <h1>This is <strong>really</strong> <strong>very</strong>important</h1>
    <h1>This is <em>really<strong>very</strong></em>important.</h1>

    <h1>This is a <em>important</em> heading </h1>
    <p>This is a <em>important</em> paragraph.</p>

    <h1>adas</h1>
    <h2>dasda</h2>
    <h3>dasdasd</h3>

    <a href="success.html">链接1</a>
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